How to lazy init class member without a default constructor

How do I lazy init class members without a default constructor?

Here is the minimum reproducible example:

#include <stdio.h>
#include <string>
#include <iostream>
using namespace std;
class B{
public:
    string name;
    B(string n):name(n){
        cout <<"B construct by name" <<endl;
    };
    B(){
        cout <<"B construct by deafult" <<endl;
    }
};
class A{
public:
    B b;
    A(){
        this->b = B{"name"}; 
        /* 
          I want to set this->b here, 
          not set by init list, 
          without B deafult construct(happen when A delcare).
        */
    };
};
int main()
{
    A a;
    return 0;
}

If you run the minimum reproducible example, it would print:

B construct by default
B construct by name

Can avoid the first log? Should I use std::optional, or is my design, as it is, is fundamentally wrong?

I want to set this->b here, not set by init list...

One other option with modern C++ is to use in-class initializer as shown below.

class B{
public:
    string name;
    B(string n):name(n){
        cout <<"B construct by name" <<endl;
    };
    B(){
        cout <<"B construct by deafult" <<endl;
    }
};
class A{
public:
    B b{"name"}; //use in-class initializer
    A(){
    
    };
};

Now the output is as you want:

B construct by name

Working demo